Preparation of monoesters of trimellitic acid



United States Patent 3,130,220 PREPARAIISN 0F MfiNGESTERS 0F TREMELLlTiQ AClD Richard E. Van Strien, Griffith, and Beniamin A. Bolton,

Gary, Ind, assignors to Standard @ii Company, Chicago, Ill, a corporation of lndiana No Drawing. Filed Apr. 15, 1959, Ser. No. 806,417 19 Claims. (CE. 260-475) This invention relates to certain monoesters of trimellitic acid and particularly to an economical process for preparation of these esters.

The monoester product of trimellitic anhydride and lower molecular weight alkanols are solid products. It is very difiicult to obtain these monesters directly in any appreciable yield because the esterification zone becomes a mass of solid material very shortly after the reaction begins and the esterification cannot be carried to completion, but high yields of the monoesters can be obtained by the use of very large excess of alcohol but only at the cost of making diesters and triesters.

An object of the invention is a process for making certain monoesters of trimellitic acid in good yield by direct reaction of anhydride and alkanol. Another object is a process of preparing certain monoesters of trimellitic acid essentially without formation of higher esters. Other objects will become apparent in the course of the detailed description of the invention.

In the process of the invention trimellitic anhydride, an alkanol containing from 1 to about 15 carbon atoms, and a liquid which is inert with respect to reaction with either the anhydride or the alkanol and which possesses appreciable solubility for the desired monoester product are intermingled. A sufiicient amount of the inert liquid is present in the esterification zone to permit forming of a slurry condition such that the contents of the zone may be readily intermingled by conventional agitating means. More than the minimum amount of inert liquid may be present with benefits on shortened esterification time but at some disability owing to the need for removal of the larger amount of inert liquid in the recovery of the monoester product.

The materials in the esterification zone are intermingled at a temperature from about 150 F. to about 350 F. The temperature utilized will be that which gives fastest reaction time with least operational complications such as the need to operate under superatmospheric pressure and/ or reflux condensation equipment. In general it is preferred to operate at temperature from about 200 to 250 'F.

The materials are intermingled at the particular temperature until essentially all of the trimellitic anhydride has been converted to the monoester of trimellitic acid. The time of reaction is dependent upon temperature primarily, but also upon tre type of alkanol and type of inert liquid present in the esterification zone.

The alkanols utilized in the process contain from 1 to about 15 carbon atoms. Examples of these alkanols are methanol, ethanol, propanol, butanol, hexanol, decanol, tridecanol and pentadecanol. A particularly useful monoester is prepared by utilizing as the alkanol the mixture of alcohols known as oxo alcohols and available commercially in C C C and C carbon atom content. These alcohols are available commercially under the names, respectively, isooctyl, isononyl, isodecyl and isotridecyl alcohols.

The inert liquid which possesses appreciable solubility for the monoester product may be a lower boiling benzene hydrocarbon, a lower boiling ketone, or a lower boiling ether. These lower boiling liquids are to be understood as materials which boil within the range of reaction tem- 3,130,220 Patented Apr. 21, 1964 peratures taught either at ordinary pressure or at slight superatrnospheric pressure. Examples of these ketones and ethers are pro-pyl ether, butyl ether, methyl ethyl ketone, diethyl ketone and methyl butyl ketone. The lower boiling benzene hydrocarbons are preferred inert liquids; examples of these are benzenes, toluene, ethylbenzene, xylene and propylbenzene.

The alkanol and trimellitic anhydride are charged to the esterification zone in a mole ratio of alkanolzanhydride of at least 1. An excess of alkanol helps in the conversion essentially completely of the anhydride. The upper limit of the mole ratio of alkanolzanhydride is about 1.3: 1. Particularly good results with the lower range of alkanols are obtained at an alkanolzanhydride ratio of about 1.5: 1.

Example I Trimellitic anhydride and n-butanol in a mole ratio of 1.15 moles of butanol per mole of anhydride were charged to a flask provided with a reflux condenser and a motor driven stirrer. Toluene was charged to the flask in an amount of 20% by Volume based on the alcohol present. The contents of the flask were vigorously intermingled by a propeller while the flask was maintained at a tempera ture between 200250 F. At the end of one hour the reaction was complete as evidenced by product water removed from the system by way of the condenser. The contents of the flask which were a mobile slurry were contacted with hexane. The hexane dissolved the toluene and unreacted butanol. Hot water removed the very slight amount of unreacted trimellitic arrhydride, leaving a product mixture of l-n-butyl trimellitate and Z-n-butyl trimellitate.

Example ll tilizing the apparatus and condition of Example I commercial isooctyl alcoholoxo productwas reacted with trimellitic anhydride to produce a mixture of 1-isooctyl trimellitate and 2-isooctyl trimellitate.

T est 111 It was attempted to prepare the n-butyl ester product and the isooctyl ester product of trimellitic acid without the presence of toluene util zing the apparatus and temperature conditions of Examples I and II. Almost immediately after reaction began the solid monoester product interferred with the contacting of the anhydride and the alcohol. Within a few minutes the flask contained an apparently solid mass of material which could not be broken-up by the motor driven propeller and the reaction stopped. Only a very small yield of the monoester product was obtained in these tests as contrasted with the essentially quantitative yield obtained in Examples I and 11.

These mono alkyl trimellitates are particularly useful as intermediates because of the presence of two carboxyl groups. They are of particular utility in the preparation of rust inhibitors for petroleum oils and in the preparation of wetting agents of all types.

Thus having described the invention what is claimed is:

1. A process for preparing monoesters of trimellitic acid which process comprises monoesterifying trimellitic anhydride with an alcohol of the type ROH where R is an alkyl of 1-15 carbons, in a mole ratio of alcohol:anhydride of 11.3:1 at a temperature from about F. to about 350 F., for the time needed to convert essentially all of said anhydride to monoester of trimellitic acid, wherein said anhydride and said alcohol are intermingled with an inert, liquid, possessing appreciable solubility for said monoester, which liquid is selected from the class consisting of lower boiling benzene hydrocarbons, ketones and ethers, said liquid being present in an amount at least sufiicient to permit the formation of a readily-intermingled slurry in said esterification zone.

2. The procms of claim 1 wherein said alcohol is n- 'butanol. s

3. The process of claim '1 wherein said alcohol is isooctyl alcohol.

4. The process of claim 1 wherein said alcohol is isotridecyl alcohol.

5. The process of claim '1 wherein said liquid is toluene.

6. The process of claim 1 wherein said liquid is xylene.

7. The process of claim 1 wherein said liquid is methyl butyl ketone.

8. The process of claim 1 wherein said liquid is butyl which process comprises reacting trimellitic anhydride with n-butanol in a mole ratio of butanolzanhydride of about 1.15:1 by intermingling said anhydride, said buta- 1101 and toluene, said toluene being present in an amount of about 20 volume percentpbased on said 'butanol, at a temperature from about 200 to 250 F. for a time to convert essentially all of said anhydride to mono-n-butyl trimellitate and recovering said ester from said toluene and said butanol.

References Cited in the file of this patent UNITED STATES PATENTS 1,779,688 Bannister Oct. 28, 1930 2,820,771 Passedouet Jan. 21, 1958 2,880,230 Edwards et a1. Mar. 31, 1959 OTHER REFERENCES Wegscheider et al.: Monatsh. fur Chemie, volume 31, pp. 1253-1301 (1910).

Wegscheider et al.: Chemical Abstracts, volume 5, pp. 1175-7 (1911).

MacArdle: The Use of Solvents in Synthetic Organic 20 Chemistry (New York, 1925), pp. 1-3. 

1. A PROCESS FOR PREPARING MONOESTERS OF TRIMELLITIC ACID WHICH PROCESS COMPRISES MONOESTERIFYING TRIMELLITIC ANHYDRIDE WITH AN ALCOHOL OF THE TYPE ROH WHERE R IS AN ALKYL OF 1-15 CARBONS, IN A MOLE RATIO OF ALCOHOL:ANHYDRIDE OF 1-1.3:1 AT A TEMPERATURE FROM ABOUT 150*F. TO ABOUT 350*F., FOR THE TIME NEEDED TO CONVERT ESSENTIALLY ALL OF SAID ANHYDRIDE TO MONOESTER OF TRIMELLITIC ACID, WHEREIN SAID ANHYDRIDE AND SAID ALCOHOL ARE INTERMINGLED WITH AN INERT, LIQUID, POSSESSING APPRECIABLE SOLUBILITY FOR SAID MONOESTER, WHICH LIQUID IS SELECTED FROM THE CLASS CONSISTING OF LOWER BOILING BENZENE HYDROCARBONS, KETONES AND ETHERS, SAID LIQUID BEING PRESENT IN AN AMOUNT AT LEAST SUFFICIENT TO PERMIT THE FORMATION OF A READILY-INTERMINGLED SLURRY IN SAID ESTERIFICATION ZONE. 